Method for performing beam search or beam transmission in wireless communication system

ABSTRACT

An embodiment of the present invention relates to a method for performing beam search or beam transmission by a first UE in a wireless communication system, the method comprising the steps of: receiving location information from a second UE; and performing at least one of beam search and beam transmission for an area determined on the basis of the received location information, wherein one or more of a beam direction, a beam first search direction, and a beam width for the beam search or the beam transmission are determined according to one or more of a location, a speed, and a moving direction of the first UE, and a service and a required packet delay value for the first UE.

TECHNICAL FIELD

The present invention relates to a wireless communication system, andmore particularly, to a method and apparatus for performing beamsearching or beam transmission.

BACKGROUND ART

Wireless communication systems have been widely deployed to providevarious types of communication services such as voice or data. Ingeneral, a wireless communication system is a multiple access systemthat supports communication of multiple users by sharing availablesystem resources (a bandwidth, transmission power, etc.) among them. Forexample, multiple access systems include a Code Division Multiple Access(CDMA) system, a Frequency Division Multiple Access (FDMA) system, aTime Division Multiple Access (TDMA) system, an Orthogonal FrequencyDivision Multiple Access (OFDMA) system, a Single Carrier FrequencyDivision Multiple Access (SC-FDMA) system, and a Multi-Carrier FrequencyDivision Multiple Access (MC-FDMA) system.

Device-to-Device (D2D) communication means a communication system fordirectly exchanging audio, data and the like between user equipmentswithout passing through a base station (evolved NodeB: eNB) byestablishing a direct link between the user equipments. D2Dcommunication may include such a system as a UE-to-UE (userequipment-to-user equipment) communication, Peer-to-Peer communicationand the like. And, the D2D communication system may be applicable to M2M(Machine-to-Machine) communication, MTC (Machine Type Communication) andthe like.

D2D communication is currently considered as one of schemes for settinga load put on a base station due to the rapidly increasing data traffic.For instance, according to D2D communication, unlike an existingwireless communication system, since data is exchanged between deviceswithout passing through a base station, overload of a network can bereduced. Moreover, by introducing D2D communication, it is able toexpect effects such as procedure reduction of a base station, powerconsumption reduction of devices involved in D2D, data transmissionspeed increase, reception capability increase of a network, loaddistribution, extension of cell coverage and the like.

Currently, discussion on V2X (Vehicle to Everything) communication is inprogress in a form associated with D2D communication. The V2Xcommunication corresponds to a concept including V2V communicationbetween vehicle UEs, V2P communication between a vehicle and a UE of adifferent type, and V2I communication between a vehicle and an RSU(roadside unit).

DISCLOSURE OF THE INVENTION Technical Task

The technical task of the present invention is to provide a method forperforming beam searching or beam transmission by reflecting thecharacteristics of V2X communication.

Technical tasks obtainable from the present invention are non-limited bythe above-mentioned technical task. And, other unmentioned technicaltasks can be clearly understood from the following description by thosehaving ordinary skill in the technical field to which the presentinvention pertains.

Technical Solution

In an aspect of the present invention, provided is a method forperforming beam searching or beam transmission by a first UE in awireless communication system. The method may include: receivinglocation information from a second UE; and performing either or both ofthe beam searching and beam transmission for an area determined based onthe received location information. In this case, at least one of a beamdirection, a preferential beam searching direction, and a beam width forthe beam searching or beam transmission may be determined according toat least one of a location, a speed, a moving direction, a service, anda packet latency requirement of the first UE.

In another aspect of the present invention, provided is a first UEdevice for performing beam searching or beam transmission in a wirelesscommunication system. The first UE device may include: a transmittingmodule; a receiving module; and a processor. In this case, the processormay be configured to receive location information from a second UEthrough the receiving module and perform either or both of the beamsearching and beam transmission for an area determined based on thereceived location information, and at least one of a beam direction, apreferential beam searching direction, and a beam width for the beamsearching or beam transmission may be determined according to at leastone of a location, a speed, a moving direction, a service, and a packetlatency requirement of the first UE.

A frequency band in which the location information is received may belower than a frequency band in which the either or both of the beamsearching and beam transmission is performed.

The location information may be included in control information.

The location information may be valid only during a timer periodindicated by a time stamp transmitted together with the locationinformation.

When the first UE is in a parking lot, the beam direction may includeall directions.

When the first UE is on a highway, the preferential beam searchingdirection may cover a smaller area than when the first UE is on a normalroad.

When the first UE is on a highway, the beam width may be smaller thanwhen the first UE is on a normal road.

As the speed of the first UE increases, the beam width for the beamsearching decreases.

The moving direction of the first UE may change the at least one of thebeam direction, the preferential beam searching direction, and the beamwidth.

The moving direction may be determined by at least one of a turn signalindicator of the first UE and a second of the first UE.

When the service relates to a safety message, the beam width mayincrease compared to when the service relates to other messages ratherthan the safety message.

When the packet latency requirement is low, the beam width may decreasecompared to when the packet latency requirement is high.

The first UE may be a Vehicle User Equipment (VUE).

Advantageous Effects

According to the present invention, it is possible to reduce theoverhead of beam searching or beam transmission.

Effects obtainable from the present invention are non-limited by theabove mentioned effect. And, other unmentioned effects can be clearlyunderstood from the following description by those having ordinary skillin the technical field to which the present invention pertains.

DESCRIPTION OF DRAWINGS

The accompanying drawings, which are included to provide a furtherunderstanding of the invention and are incorporated in and constitute apart of this specification, illustrate embodiments of the invention andtogether with the description serve to explain the principles of theinvention.

FIG. 1 is a diagram for a structure of a radio frame;

FIG. 2 is a diagram for a resource grid in a downlink slot;

FIG. 3 is a diagram for a structure of a downlink subframe;

FIG. 4 is a diagram for a structure of an uplink subframe;

FIG. 5 is a diagram for a configuration of a wireless communicationsystem having multiple antennas;

FIG. 6 is a diagram for a subframe in which a D2D synchronization signalis transmitted;

FIG. 7 is a diagram for explaining relay of a D2D signal;

FIG. 8 is a diagram for an example of a D2D resource pool for performingD2D communication;

FIG. 9 is a diagram for explaining an SA period;

FIG. 10 illustrates a frame structure for new Radio Access Technology(RAT);

FIGS. 11 to 13 are diagrams for explaining various embodiments of thepresent invention; and

FIG. 14 is a diagram for configurations of a transmitter and a receiver.

BEST MODE FOR INVENTION

The embodiments of the present invention described hereinbelow arecombinations of elements and features of the present invention. Theelements or features may be considered selective unless otherwisementioned. Each element or feature may be practiced without beingcombined with other elements or features. Further, an embodiment of thepresent invention may be constructed by combining parts of the elementsand/or features. Operation orders described in embodiments of thepresent invention may be rearranged. Some constructions or features ofany one embodiment may be included in another embodiment and may bereplaced with corresponding constructions or features of anotherembodiment.

In the embodiments of the present invention, a description is made,centering on a data transmission and reception relationship between aBase Station (BS) and a User Equipment (UE). The BS is a terminal nodeof a network, which communicates directly with a UE. In some cases, aspecific operation described as performed by the BS may be performed byan upper node of the BS.

Namely, it is apparent that, in a network comprised of a plurality ofnetwork nodes including a BS, various operations performed forcommunication with a UE may be performed by the BS or network nodesother than the BS. The term ‘BS’ may be replaced with the term ‘fixedstation’, ‘Node B’, ‘evolved Node B (eNode B or eNB)’, ‘Access Point(AP)’, etc. The term ‘relay’ may be replaced with the term ‘Relay Node(RN)’ or ‘Relay Station (RS)’. The term ‘terminal’ may be replaced withthe term ‘UE’, ‘Mobile Station (MS)’, ‘Mobile Subscriber Station (MSS)’,‘Subscriber Station (SS)’, etc.

The term “cell”, as used herein, may be applied to transmission andreception points such as a base station (eNB), sector, remote radio head(RRH) and relay, and may also be extensively used by a specifictransmission/reception point to distinguish between component carriers.

Specific terms used for the embodiments of the present invention areprovided to help the understanding of the present invention. Thesespecific terms may be replaced with other terms within the scope andspirit of the present invention.

In some cases, to prevent the concept of the present invention frombeing ambiguous, structures and apparatuses of the known art will beomitted, or will be shown in the form of a block diagram based on mainfunctions of each structure and apparatus. Also, wherever possible, thesame reference numbers will be used throughout the drawings and thespecification to refer to the same or like parts.

The embodiments of the present invention can be supported by standarddocuments disclosed for at least one of wireless access systems,Institute of Electrical and Electronics Engineers (IEEE) 802, 3rdGeneration Partnership Project (3GPP), 3GPP Long Term Evolution (3GPPLTE), LTE-Advanced (LTE-A), and 3GPP2. Steps or parts that are notdescribed to clarify the technical features of the present invention canbe supported by those documents. Further, all terms as set forth hereincan be explained by the standard documents.

Techniques described herein can be used in various wireless accesssystems such as Code Division Multiple Access (CDMA), Frequency DivisionMultiple Access (FDMA), Time Division Multiple Access (TDMA), OrthogonalFrequency Division Multiple Access (OFDMA), Single Carrier-FrequencyDivision Multiple Access (SC-FDMA), etc. CDMA may be implemented as aradio technology such as Universal Terrestrial Radio Access (UTRA) orCDMA2000. TDMA may be implemented as a radio technology such as GlobalSystem for Mobile communications (GSM)/General Packet Radio Service(GPRS)/Enhanced Data Rates for GSM Evolution (EDGE). OFDMA may beimplemented as a radio technology such as IEEE 802.11 (Wi-Fi), IEEE802.16 (WiMAX), IEEE 802.20, Evolved-UTRA (E-UTRA) etc. UTRA is a partof Universal Mobile Telecommunications System (UMTS). 3GPP LTE is a partof Evolved UMTS (E-UMTS) using E-UTRA. 3GPP LTE employs OFDMA fordownlink and SC-FDMA for uplink. LTE-A is an evolution of 3GPP LTE.WiMAX can be described by the IEEE 802.16e standard (WirelessMetropolitan Area Network (WirelessMAN)-OFDMA Reference System) and theIEEE 802.16m standard (WirelessMAN-OFDMA Advanced System). For clarity,this application focuses on the 3GPP LTE and LTE-A systems. However, thetechnical features of the present invention are not limited thereto.

LTE/LTE-A Resource Structure/Channel

With reference to FIG. 1, the structure of a radio frame will bedescribed below.

In a cellular Orthogonal Frequency Division Multiplexing (OFDM) wirelessPacket communication system, uplink and/or downlink data Packets aretransmitted in subframes. One subframe is defined as a predeterminedtime period including a plurality of OFDM symbols. The 3GPP LTE standardsupports a type-1 radio frame structure applicable to Frequency DivisionDuplex (FDD) and a type-2 radio frame structure applicable to TimeDivision Duplex (TDD).

FIG. 1(a) illustrates the type-1 radio frame structure. A downlink radioframe is divided into 10 subframes. Each subframe is further dividedinto two slots in the time domain. A unit time during which one subframeis transmitted is defined as a Transmission Time Interval (TTI). Forexample, one subframe may be 1 ms in duration and one slot may be 0.5 msin duration. A slot includes a plurality of OFDM symbols in the timedomain and a plurality of Resource Blocks (RBs) in the frequency domain.Because the 3GPP LTE system adopts OFDMA for downlink, an OFDM symbolrepresents one symbol period. An OFDM symbol may be referred to as anSC-FDMA symbol or symbol period. An RB is a resource allocation unitincluding a plurality of contiguous subcarriers in a slot.

The number of OFDM symbols in one slot may vary depending on a CyclicPrefix (CP) configuration. There are two types of CPs: extended CP andnormal CP. In the case of the normal CP, one slot includes 7 OFDMsymbols. In the case of the extended CP, the length of one OFDM symbolis increased and thus the number of OFDM symbols in a slot is smallerthan in the case of the normal CP. Thus when the extended CP is used,for example, 6 OFDM symbols may be included in one slot. If channelstate gets poor, for example, during fast movement of a UE, the extendedCP may be used to further decrease Inter-Symbol Interference (ISI).

In the case of the normal CP, one subframe includes 14 OFDM symbolsbecause one slot includes 7 OFDM symbols. The first two or three OFDMsymbols of each subframe may be allocated to a Physical Downlink ControlCHannel (PDCCH) and the other OFDM symbols may be allocated to aPhysical Downlink Shared Channel (PDSCH).

FIG. 1(b) illustrates the type-2 radio frame structure. A type-2 radioframe includes two half frames, each having 5 subframes, a DownlinkPilot Time Slot (DwPTS), a Guard Period (GP), and an Uplink Pilot TimeSlot (UpPTS). Each subframe is divided into two slots. The DwPTS is usedfor initial cell search, synchronization, or channel estimation at a UE.The UpPTS is used for channel estimation and acquisition of uplinktransmission synchronization to a UE at an eNB. The GP is a periodbetween an uplink and a downlink, which eliminates uplink interferencecaused by multipath delay of a downlink signal. One subframe includestwo slots irrespective of the type of a radio frame.

The above-described radio frame structures are purely exemplary and thusit is to be noted that the number of subframes in a radio frame, thenumber of slots in a subframe, or the number of symbols in a slot mayvary.

FIG. 2 illustrates the structure of a downlink resource grid for theduration of one downlink slot. A downlink slot includes 7 OFDM symbolsin the time domain and an RB includes 12 subcarriers in the frequencydomain, which does not limit the scope and spirit of the presentinvention. For example, a downlink slot may include 7 OFDM symbols inthe case of the normal CP, whereas a downlink slot may include 6 OFDMsymbols in the case of the extended CP. Each element of the resourcegrid is referred to as a Resource Element (RE). An RB includes 12×7 REs.The number of RBs in a downlink slot, NDL depends on a downlinktransmission bandwidth. An uplink slot may have the same structure as adownlink slot.

FIG. 3 illustrates the structure of a downlink subframe. Up to threeOFDM symbols at the start of the first slot in a downlink subframe areused for a control region to which control channels are allocated andthe other OFDM symbols of the downlink subframe are used for a dataregion to which a PDSCH is allocated. Downlink control channels used inthe 3GPP LTE system include a Physical Control Format Indicator CHannel(PCFICH), a Physical Downlink Control CHannel (PDCCH), and a PhysicalHybrid automatic repeat request (HARQ) Indicator CHannel (PHICH). ThePCFICH is located in the first OFDM symbol of a subframe, carryinginformation about the number of OFDM symbols used for transmission ofcontrol channels in the subframe. The PHICH delivers an HARQACKnowledgment/Negative ACKnowledgment (ACK/NACK) signal in response toan uplink transmission. Control information carried on the PDCCH iscalled Downlink Control Information (DCI). The DCI transports uplink ordownlink scheduling information, or uplink transmission power controlcommands for UE groups. The PDCCH delivers information about resourceallocation and a transport format for a Downlink Shared CHannel(DL-SCH), resource allocation information about an Uplink Shared CHannel(UL-SCH), paging information of a Paging CHannel (PCH), systeminformation on the DL-SCH, information about resource allocation for ahigher-layer control message such as a Random Access Responsetransmitted on the PDSCH, a set of transmission power control commandsfor individual UEs of a UE group, transmission power controlinformation, Voice Over Internet Protocol (VoIP) activation information,etc. A plurality of PDCCHs may be transmitted in the control region. AUE may monitor a plurality of PDCCHs. A PDCCH is formed by aggregatingone or more consecutive Control Channel Elements (CCEs). A CCE is alogical allocation unit used to provide a PDCCH at a coding rate basedon the state of a radio channel. A CCE includes a plurality of REgroups. The format of a PDCCH and the number of available bits for thePDCCH are determined according to the correlation between the number ofCCEs and a coding rate provided by the CCEs. An eNB determines the PDCCHformat according to DCI transmitted to a UE and adds a Cyclic RedundancyCheck (CRC) to control information. The CRC is masked by an Identifier(ID) known as a Radio Network Temporary Identifier (RNTI) according tothe owner or usage of the PDCCH. If the PDCCH is directed to a specificUE, its CRC may be masked by a cell-RNTI (C-RNTI) of the UE. If thePDCCH is for a paging message, the CRC of the PDCCH may be masked by aPaging Indicator Identifier (P-RNTI). If the PDCCH carries systeminformation, particularly, a System Information Block (SIB), its CRC maybe masked by a system information ID and a System Information RNTI(SI-RNTI). To indicate that the PDCCH carries a Random Access Responsein response to a Random Access Preamble transmitted by a UE, its CRC maybe masked by a Random Access-RNTI (RA-RNTI).

FIG. 4 illustrates the structure of an uplink subframe. An uplinksubframe may be divided into a control region and a data region in thefrequency domain. A Physical Uplink Control CHannel (PUCCH) carryinguplink control information is allocated to the control region and aPhysical Uplink Shared Channel (PUSCH) carrying user data is allocatedto the data region. To maintain the property of a single carrier, a UEdoes not transmit a PUSCH and a PUCCH simultaneously. A PUCCH for a UEis allocated to an RB pair in a subframe. The RBs of the RB pair occupydifferent subcarriers in two slots. Thus it is said that the RB pairallocated to the PUCCH is frequency-hopped over a slot boundary.

Reference Signals (RSs)

In a wireless communication system, a Packet is transmitted on a radiochannel. In view of the nature of the radio channel, the Packet may bedistorted during the transmission. To receive the signal successfully, areceiver should compensate for the distortion of the received signalusing channel information. Generally, to enable the receiver to acquirethe channel information, a transmitter transmits a signal known to boththe transmitter and the receiver and the receiver acquires knowledge ofchannel information based on the distortion of the signal received onthe radio channel. This signal is called a pilot signal or an RS.

In the case of data transmission and reception through multipleantennas, knowledge of channel states between Transmission (Tx) antennasand Reception (Rx) antennas is required for successful signal reception.Accordingly, an RS should be transmitted through each Tx antenna.

RSs may be divided into downlink RSs and uplink RSs. In the current LTEsystem, the uplink RSs include:

i) DeModulation-Reference Signal (DM-RS) used for channel estimation forcoherent demodulation of information delivered on a PUSCH and a PUCCH;and

ii) Sounding Reference Signal (SRS) used for an eNB or a network tomeasure the quality of an uplink channel in a different frequency.

The downlink RSs are categorized into:

i) Cell-specific Reference Signal (CRS) shared among all UEs of a cell;

ii) UE-specific RS dedicated to a specific UE;

iii) DM-RS used for coherent demodulation of a PDSCH, when the PDSCH istransmitted;

iv) Channel State Information-Reference Signal (CSI-RS) carrying CSI,when downlink DM-RSs are transmitted;

v) Multimedia Broadcast Single Frequency Network (MBSFN) RS used forcoherent demodulation of a signal transmitted in MBSFN mode; and

vi) positioning RS used to estimate geographical position informationabout a UE.

RSs may also be divided into two types according to their purposes: RSfor channel information acquisition and RS for data demodulation. Sinceits purpose lies in that a UE acquires downlink channel information, theformer should be transmitted in a broad band and received even by a UEthat does not receive downlink data in a specific subframe. This RS isalso used in a situation like handover. The latter is an RS that an eNBtransmits along with downlink data in specific resources. A UE candemodulate the data by measuring a channel using the RS. This RS shouldbe transmitted in a data transmission area.

Modeling of MIMO System

FIG. 5 is a diagram illustrating a configuration of a wirelesscommunication system having multiple antennas.

As shown in FIG. 5(a), if the number of transmit antennas is increasedto NT and the number of receive antennas is increased to NR, atheoretical channel transmission capacity is increased in proportion tothe number of antennas, unlike the case where a plurality of antennas isused in only a transmitter or a receiver. Accordingly, it is possible toimprove a transfer rate and to remarkably improve frequency efficiency.As the channel transmission capacity is increased, the transfer rate maybe theoretically increased by a product of a maximum transfer rate Roupon utilization of a single antenna and a rate increase ratio Ri.

R _(i)=min(N _(T) ,N _(R))  [Equation 1]

For instance, in an MIMO communication system, which uses 4 transmitantennas and 4 receive antennas, a transmission rate 4 times higher thanthat of a single antenna system can be obtained. Since this theoreticalcapacity increase of the MIMO system has been proved in the middle of90's, many ongoing efforts are made to various techniques tosubstantially improve a data transmission rate. In addition, thesetechniques are already adopted in part as standards for various wirelesscommunications such as 3G mobile communication, next generation wirelessLAN and the like.

The trends for the MIMO relevant studies are explained as follows. Firstof all, many ongoing efforts are made in various aspects to develop andresearch information theory study relevant to MIMO communicationcapacity calculations and the like in various channel configurations andmultiple access environments, radio channel measurement and modelderivation study for MIMO systems, spatiotemporal signal processingtechnique study for transmission reliability enhancement andtransmission rate improvement and the like.

In order to explain a communicating method in an MIMO system in detail,mathematical modeling can be represented as follows. It is assumed thatthere are NT transmit antennas and NR receive antennas.

Regarding a transmitted signal, if there are NT transmit antennas, themaximum number of pieces of information that can be transmitted is NT.Hence, the transmission information can be represented as shown inEquation 2.

S=└s ₁ ,s ₂ , . . . ,s _(N) _(T) ┘^(T)  [Equation 2]

Meanwhile, transmit powers can be set different from each other forindividual pieces of transmission information s₁, s₂, . . . , s_(N) _(T), respectively. If the transmit powers are set to P₁, P₂, A, P_(N) _(T), respectively, the transmission information with adjusted transmitpowers can be represented as Equation 3.

ŝ=[ŝ ₁ ,ŝ ₂ , . . . ,s _(N) _(T) ]^(T)=[P ₁ s ₁ ,P ₂ s ₂ , . . . ,P _(N)_(T) s _(N) _(T) ]^(T)  [Equation 3]

In addition, Ŝ can be represented as Equation 4 using diagonal matrix Pof the transmission power.

$\begin{matrix}{\hat{s} = {{\begin{bmatrix}P_{1} & \; & \; & 0 \\\; & P_{2} & \; & \; \\\; & \; & \ddots & \; \\0 & \; & \; & P_{N_{T}}\end{bmatrix}\begin{bmatrix}s_{1} \\s_{2} \\\vdots \\s_{N_{T}}\end{bmatrix}} = {Ps}}} & \left\lbrack {{Equation}\mspace{14mu} 4} \right\rbrack\end{matrix}$

Assuming a case of configuring NT transmitted signals x₁, x₂, . . . ,x_(N) _(T) , which are actually transmitted, by applying weight matrix Wto the information vector Ŝ having the adjusted transmit powers, theweight matrix w serves to appropriately distribute the transmissioninformation to each antenna according to a transport channel state. x₁,x₂, . . . , x_(N) _(T) can be expressed by using the vector X asfollows.

$\begin{matrix}{x = {\quad{\begin{bmatrix}x_{1} \\x_{2} \\\vdots \\x_{i} \\\vdots \\x_{N_{T}}\end{bmatrix} = {{\begin{bmatrix}w_{11} & w_{12} & \ldots & w_{1N_{T}} \\w_{21} & w_{22} & \ldots & w_{2N_{T}} \\\vdots & \; & \ddots & \; \\w_{i\; 1} & w_{i\; 2} & \ldots & w_{{iN}_{T}} \\\vdots & \; & \ddots & \; \\w_{N_{T}1} & w_{N_{T}2} & \ldots & w_{N_{T}N_{T}}\end{bmatrix}\begin{bmatrix}{\hat{s}}_{1} \\{\hat{s}}_{2} \\\vdots \\{\hat{s}}_{j} \\\vdots \\{\hat{s}}_{N_{T}}\end{bmatrix}} = {{W\; \hat{s}} = {WPs}}}}}} & \left\lbrack {{Equation}\mspace{14mu} 5} \right\rbrack\end{matrix}$

In Equation 5, w_(ij) denotes a weight between an i^(th) transmitantenna and j^(th) information. W is also called a precoding matrix.

If the NR receive antennas are present, respective received signals y₁,y₂, . . . , y_(N) _(R) of the antennas can be expressed as follows.

y=[y ₁ ,y ₂ , . . . ,y _(N) _(R) ]^(T)  [Equation 6]

If channels are modeled in the MIMO wireless communication system, thechannels may be distinguished according to transmit/receive antennaindexes. A channel from the transmit antenna j to the receive antenna iis denoted by h_(ij). In h_(ij), it is noted that the indexes of thereceive antennas precede the indexes of the transmit antennas in view ofthe order of indexes.

FIG. 5(b) is a diagram illustrating channels from the NT transmitantennas to the receive antenna i. The channels may be combined andexpressed in the form of a vector and a matrix. In FIG. 5(b), thechannels from the NT transmit antennas to the receive antenna i can beexpressed as follows.

h _(i) ^(T)=[h _(i1) ,h _(i2) , . . . ,h _(iN) _(T) ]  [Equation 7]

Accordingly, all channels from the NT transmit antennas to the NRreceive antennas can be expressed as follows.

$\begin{matrix}{H = {\begin{bmatrix}h_{1}^{T} \\h_{2}^{T} \\\vdots \\h_{i}^{T} \\\vdots \\h_{N_{R}}^{T}\end{bmatrix} = \begin{bmatrix}h_{11} & h_{12} & \ldots & h_{1N_{T}} \\h_{21} & h_{22} & \ldots & h_{2N_{T}} \\\vdots & \; & \ddots & \; \\h_{i\; 1} & h_{i\; 2} & \ldots & h_{{iN}_{T}} \\\vdots & \; & \ddots & \; \\h_{N_{R}1} & h_{N_{R}2} & \ldots & h_{N_{R}N_{T}}\end{bmatrix}}} & \left\lbrack {{Equation}\mspace{14mu} 8} \right\rbrack\end{matrix}$

An AWGN (Additive White Gaussian Noise) is added to the actual channelsafter a channel matrix H. The AWGN n₁, n₂, . . . , n_(N) _(R)respectively added to the NR receive antennas can be expressed asfollows.

n=[n ₁ ,n ₂ , . . . ,n _(N) _(R) ]^(T)  [Equation 9]

Through the above-described mathematical modeling, the received signalscan be expressed as follows.

$\begin{matrix}{y = {\begin{bmatrix}y_{1} \\y_{2} \\\vdots \\y_{i} \\\vdots \\y_{N_{R}}\end{bmatrix} = {{{\begin{bmatrix}h_{11} & h_{12} & \ldots & h_{1N_{T}} \\h_{21} & h_{22} & \ldots & h_{2N_{T}} \\\vdots & \; & \ddots & \; \\h_{i\; 1} & h_{i\; 2} & \ldots & h_{{iN}_{T}} \\\vdots & \; & \ddots & \; \\h_{N_{R}1} & h_{N_{R}2} & \ldots & h_{N_{R}N_{T}}\end{bmatrix}\begin{bmatrix}x_{1} \\x_{2} \\\vdots \\x_{j} \\\vdots \\x_{N_{T}}\end{bmatrix}} + \begin{bmatrix}n_{1} \\n_{2} \\\vdots \\n_{i} \\\vdots \\n_{N_{R}}\end{bmatrix}} = {{Hx} + n}}}} & \left\lbrack {{Equation}\mspace{14mu} 10} \right\rbrack\end{matrix}$

Meanwhile, the number of rows and columns of the channel matrix Hindicating the channel state is determined by the number of transmit andreceive antennas. The number of rows of the channel matrix H is equal tothe number NR of receive antennas and the number of columns thereof isequal to the number NR of transmit antennas. That is, the channel matrixH is an NR×NT matrix.

The rank of the matrix is defined by the smaller of the number of rowsand the number of columns, which are independent from each other.Accordingly, the rank of the matrix is not greater than the number ofrows or columns. The rank rank(H) of the channel matrix H is restrictedas follows.

rank(H)≤min(N _(T) ,N _(R))  [Equation 11]

Additionally, the rank of a matrix can also be defined as the number ofnon-zero Eigen values when the matrix is Eigen-value-decomposed.Similarly, the rank of a matrix can be defined as the number of non-zerosingular values when the matrix is singular-value-decomposed.Accordingly, the physical meaning of the rank of a channel matrix can bethe maximum number of channels through which different pieces ofinformation can be transmitted.

In the description of the present document, ‘rank’ for MIMO transmissionindicates the number of paths capable of sending signals independentlyon specific time and frequency resources and ‘number of layers’indicates the number of signal streams transmitted through therespective paths. Generally, since a transmitting end transmits thenumber of layers corresponding to the rank number, one rank has the samemeaning of the layer number unless mentioned specially.

Synchronization Acquisition of D2D UE

Now, a description will be given of synchronization acquisition betweenUEs in D2D communication based on the foregoing description in thecontext of the legacy LTE/LTE-A system. In an OFDM system, iftime/frequency synchronization is not acquired, the resulting Inter-CellInterference (ICI) may make it impossible to multiplex different UEs inan OFDM signal. If each individual D2D UE acquires synchronization bytransmitting and receiving a synchronization signal directly, this isinefficient. In a distributed node system such as a D2D communicationsystem, therefore, a specific node may transmit a representativesynchronization signal and the other UEs may acquire synchronizationusing the representative synchronization signal. In other words, somenodes (which may be an eNB, a UE, and a Synchronization Reference Node(SRN, also referred to as a synchronization source)) may transmit a D2DSynchronization Signal (D2DSS) and the remaining UEs may transmit andreceive signals in synchronization with the D2DSS.

D2DSSs may include a Primary D2DSS (PD2DSS) or a Primary SidelinkSynchronization Signal (PSSS) and a Secondary D2DSS (SD2DSS) or aSecondary Sidelink Synchronization Signal (SSSS). The PD2DSS may beconfigured to have a similar/modified/repeated structure of a Zadoff-chusequence of a predetermined length or a Primary Synchronization Signal(PSS). Unlike a DL PSS, the PD2DSS may use a different Zadoff-chu rootindex (e.g., 26, 37). And, the SD2DSS may be configured to have asimilar/modified/repeated structure of an M-sequence or a SecondarySynchronization Signal (SSS). If UEs synchronize their timing with aneNB, the eNB serves as an SRN and the D2DSS is a PSS/SSS. Unlike PSS/SSSof DL, the PD2DSS/SD2DSS follows UL subcarrier mapping scheme. FIG. 6shows a subframe in which a D2D synchronization signal is transmitted. APhysical D2D Synchronization Channel (PD2DSCH) may be a (broadcast)channel carrying basic (system) information that a UE should firstobtain before D2D signal transmission and reception (e.g., D2DSS-relatedinformation, a Duplex Mode (DM), a TDD UL/DL configuration, a resourcepool-related information, the type of an application related to theD2DSS, etc.). The PD2DSCH may be transmitted in the same subframe as theD2DSS or in a subframe subsequent to the frame carrying the D2DSS. ADMRS can be used to demodulate the PD2DSCH.

The SRN may be a node that transmits a D2DSS and a PD2DSCH. The D2DSSmay be a specific sequence and the PD2DSCH may be a sequencerepresenting specific information or a codeword produced bypredetermined channel coding. The SRN may be an eNB or a specific D2DUE. In the case of partial network coverage or out of network coverage,the SRN may be a UE.

In a situation illustrated in FIG. 7, a D2DSS may be relayed for D2Dcommunication with an out-of-coverage UE. The D2DSS may be relayed overmultiple hops. The following description is given with the appreciationthat relay of an SS covers transmission of a D2DSS in a separate formataccording to a SS reception time as well as direct Amplify-and-Forward(AF)-relay of an SS transmitted by an eNB. As the D2DSS is relayed, anin-coverage UE may communicate directly with an out-of-coverage UE.

D2D Resource Pool

FIG. 8 shows an example of a UE1, a UE2 and a resource pool used by theUE1 and the UE2 performing D2D communication. In FIG. 8 (a), a UEcorresponds to a terminal or such a network device as an eNBtransmitting and receiving a signal according to a D2D communicationscheme. A UE selects a resource unit corresponding to a specificresource from a resource pool corresponding to a set of resources andthe UE transmits a D2D signal using the selected resource unit. A UE2corresponding to a reception UE receives a configuration of a resourcepool in which the UE1 is able to transmit a signal and detects a signalof the UE1 in the resource pool. In this case, if the UE1 is located atthe inside of coverage of an eNB, the eNB can inform the UE1 of theresource pool. If the UE1 is located at the outside of coverage of theeNB, the resource pool can be informed by a different UE or can bedetermined by a predetermined resource. In general, a resource poolincludes a plurality of resource units. A UE selects one or moreresource units from among a plurality of the resource units and may beable to use the selected resource unit(s) for D2D signal transmission.FIG. 8 (b) shows an example of configuring a resource unit. Referring toFIG. 8 (b), the entire frequency resources are divided into the N_(F)number of resource units and the entire time resources are divided intothe N_(T) number of resource units. In particular, it is able to defineN_(F)*N_(T) number of resource units in total. In particular, a resourcepool can be repeated with a period of N_(T) subframes. Specifically, asshown in FIG. 8, one resource unit may periodically and repeatedlyappear. Or, an index of a physical resource unit to which a logicalresource unit is mapped may change with a predetermined patternaccording to time to obtain a diversity gain in time domain and/orfrequency domain. In this resource unit structure, a resource pool maycorrespond to a set of resource units capable of being used by a UEintending to transmit a D2D signal.

A resource pool can be classified into various types. First of all, theresource pool can be classified according to contents of a D2D signaltransmitted via each resource pool. For example, the contents of the D2Dsignal can be classified into various signals and a separate resourcepool can be configured according to each of the contents. The contentsof the D2D signal may include SA (scheduling assignment), a D2D datachannel, and a discovery channel. The SA may correspond to a signalincluding information on a resource position of a D2D data channel,information on MCS (modulation and coding scheme) necessary formodulating and demodulating a data channel, information on a MIMOtransmission scheme, information on TA (timing advance), and the like.The SA signal can be transmitted on an identical resource unit in amanner of being multiplexed with D2D data. In this case, an SA resourcepool may correspond to a pool of resources that an SA and D2D data aretransmitted in a manner of being multiplexed. The SA signal can also bereferred to as a D2D control channel or a PSCCH (physical sidelinkcontrol channel). The D2D data channel (or, PSSCH (physical sidelinkshared channel)) corresponds to a resource pool used by a transmissionUE to transmit user data. If an SA and a D2D data are transmitted in amanner of being multiplexed in an identical resource unit, D2D datachannel except SA information can be transmitted only in a resource poolfor the D2D data channel. In other word, resource elements (REs), whichare used to transmit SA information in a specific resource unit of an SAresource pool, can also be used for transmitting D2D data in a D2D datachannel resource pool. The discovery channel may correspond to aresource pool for a message that enables a neighboring UE to discovertransmission UE transmitting information such as ID of the UE, and thelike.

Although contents of D2D signal are identical to each other, it may usea different resource pool according to a transmission/receptionattribute of the D2D signal. For example, in case of the same D2D datachannel or the same discovery message, the D2D data channel or thediscovery signal can be classified into a different resource poolaccording to a transmission timing determination scheme (e.g., whether aD2D signal is transmitted at the time of receiving a synchronizationreference signal or the timing to which a prescribed timing advance isadded) of a D2D signal, a resource allocation scheme (e.g., whether atransmission resource of an individual signal is designated by an eNB oran individual transmission UE selects an individual signal transmissionresource from a pool), a signal format (e.g., number of symbols occupiedby a D2D signal in a subframe, number of subframes used for transmittinga D2D signal), signal strength from an eNB, strength of transmit powerof a D2D UE, and the like. For clarity, a method for an eNB to directlydesignate a transmission resource of a D2D transmission UE is referredto as a mode 1. If a transmission resource region is configured inadvance or an eNB designates the transmission resource region and a UEdirectly selects a transmission resource from the transmission resourceregion, it is referred to as a mode 2. In case of performing D2Ddiscovery, if an eNB directly indicates a resource, it is referred to asa type 2. If a UE directly selects a transmission resource from apredetermined resource region or a resource region indicated by the eNB,it is referred to as a type 1

Transmission and Reception of SA

A mode 1 UE can transmit an SA signal (or, a D2D control signal, SCI(sidelink control information)) via a resource configured by an eNB. Amode 2 UE receives a configured resource to be used for D2Dtransmission. The mode 2 UE can transmit SA by selecting a timefrequency resource from the configured resource.

The SA period can be defined as FIG. 9. Referring to FIG. 9, a first SAperiod can start at a subframe apart from a specific system frame asmuch as a prescribed offset (SAOffsetIndicator) indicated by higherlayer signaling. Each SA period can include an SA resource pool and asubframe pool for transmitting D2D data. The SA resource pool caninclude subframes ranging from a first subframe of an SA period to thelast subframe among subframes indicated by a subframe bitmap(saSubframeBitmap) to transmit SA. In case of mode 1, T-RPT(time-resource pattern for transmission) is applied to the resource poolfor transmitting D2D data to determine a subframe in which an actualdata is transmitted. As shown in the drawing, if the number of subframesincluded in an SA period except the SA resource pool is greater than thenumber of T-RPT bits, the T-RPT can be repeatedly applied and the lastlyapplied T-RPT can be applied in a manner of being truncated as many asthe number of remaining subframes.

Meanwhile, in V2V (vehicle to vehicle) communication, a CAM (cooperativeawareness message) of a periodic message type, a DENM (decentralizedenvironmental notification message) of an event triggered message type,and the like can be transmitted. The CAM can include dynamic statusinformation of a vehicle such as direction and velocity, static data ofa vehicle such as a size, and basic vehicle information such as externallight status, path history, and the like. A size of the CAM maycorrespond to 50 to 300 bytes. The DENM may correspond to a messagewhich is generated when an accidental status such as malfunction of avehicle, an accident, and the like occurs. A size of the DENM may beless than 3000 bytes. All vehicles located within a transmission rangeof the DENM can receive the DENM. In this case, the DENM may have apriority higher than a priority of the CAM. In this case, in the aspectof a single UE, the higher priority means that a UE preferentiallytransmits a message of a higher priority when messages are transmittedat the same time. Or, the higher priority means that a UE intends topreferentially transmit a message of a higher priority in time among aplurality of messages. In the aspect of a plurality of UEs, since amessage of a higher priority receives less interference compared to amessage of a lower priority, it may be able to lower a reception errorrate. If security overhead is included in the CAM, the CAM may have abigger message size.

NR (New RAT (Radio Access Technology))

As more and more communication devices have required highercommunication capacity, the necessity of the mobile broadbandcommunications much improved than the existing radio access technologyhas increased. In addition, massive Machine Type Communications (MTC)capable of providing various services at anytime and anywhere byconnecting a number of devices or things to each other has beenconsidered as a main issue in the next generation communication system.Moreover, communication system design capable of supporting services/UEssensitive to reliability and latency has been discussed. As describedabove, the introduction of the next generation radio access technologyconsidering the enhanced mobile broadband communication, massive MTC,Ultra-Reliable and Low Latency Communication (URLLC), etc. has beendiscussed. In the present invention, the corresponding technology isreferred to as NR.

FIG. 10 illustrates a frame structure for the NR. Referring to FIG. 10,a self-contained structure capable of including a DL control channel, DLor UL data, and a UL control channel in one frame unit can be used. Inthis case, the DL control channel may carry DL data schedulinginformation, UL data scheduling information, etc., and the UL controlchannel may carry ACK/NACK information in response to DL data, ChannelState Information (CSI) (e.g., modulation and coding scheme information,MIMO transmission related information, etc.), a scheduling request, etc.A time gap for DL-to-UL or UL-to-DL switching may exist between controland data regions. In addition, some of the DL control, DL data, UL data,and UL control may not be implemented in one frame, or the order ofchannels included in one frame may vary (for example, DL control/DLdata/UL control/UL data, UL control/UL data/DL control/DL data, etc.).

Analog Beamforming

In the mmW/mmWave system, since a wavelength is shortened, a pluralityof antennas may be installed in the same area. That is, considering thatthe wavelength at 30 GHz band is 1 cm, a total of 100 antenna elementsmay be installed in a 5 by 5 cm panel at intervals of 0.5 lambda(wavelength) in the case of a 2-dimensional array. Therefore, the mmWsystem may improve the coverage or throughput by increasing beamforming(BF) gain using multiple antenna elements.

In this case, if a transceiver unit (TXRU) is provided to each antennaelement to enable adjustment of transmit power and phase, independentbeamforming can be performed per frequency resource. However, installingTXRUs in all of the about 100 antenna elements is less feasible in termsof cost. Therefore, a method of mapping a plurality of antenna elementsto one TXRU and adjusting the direction of a beam using an analog phaseshifter has been considered. However, according to this analogbeamforming method, only one beam direction is created over the fullband so that selective beamforming is impossible.

To solve this problem, as an intermediate form of digital BF and analogBF, hybrid BF with B TXRUs that are fewer than Q antenna elements may beconsidered. In the case of the hybrid BF, the number of beam directionsthat can be transmitted at the same time is limited to B or less, whichdepends on how B TXRUs and Q antenna elements are connected.

When beamforming is applied to overcome the path loss in high bands suchas mmW, a beam searching/scanning process needs to be performed betweena transmitter and a receiver. However, in case a UE has high mobility asin V2X communication, beam matching failure, errors, etc. may occur dueto changes in the location of the UE in the beamforming process. Inaddition, if a number of UEs perform beam searching, it may causesignificant overhead. For example, as shown in FIG. 11, when V2X UEsperform beam scanning in the mmWave system, each UE should perform beamsearching with respect to too many beams. However, if all UEs performbeam searching with respect to all directions/regions, it may causesignificant overhead as described above. Therefore, to solve such aproblem, an efficient beam searching/transmission method will beexplained in the following description.

Embodiment

According to an embodiment of the present invention, a UE (first UE) canperform beam searching/beam transmission using location information of apeer UE (second UE). In other words, the first UE may receive thelocation information from the second UE and perform either or both ofthe beam searching and beam transmission for an area determined based onthe received location information. That is, using the locationinformation of the peer UE, the first UE performs a process fortransmitting a transmission beam and searching for a reception beam onlywithin the area where the peer UE is expected to be located. Inparticular, this can be applied to unicast. If the beamsearching/transmission is performed in a limited direction based on thelocation information as shown in the example of FIG. 11, the overheadthereof can be reduced.

The location information can be transmitted to the first UE, beingincluded in a control signal such as a physical layer/MAC/RRC signal.

The frequency band where the location information is transmitted may bedifferent from the frequency band where the beam searching or beamtransmission is performed for the area determined based on the locationinformation. For example, the frequency band in which the locationinformation is received may be lower than the frequency band in whicheither or both of the beam searching and beam transmission is performed.That is, neighboring UEs may share their location information bytransmitting control information using wide coverage in a low frequencyband. Alternatively, a neighboring eNB or RSU may broadcast, as thelocation information of a neighboring UE, some or all of the following:UE ID, location information, speed information, and informationindicating whether a higher-layer event occurs. Thereafter, a UE mayreceive the information of the neighboring UE from the eNB or RSU anduse the received information in setting a beam transmission/searchingdirection.

The frequency band where the location information is transmitted may beequal/similar to the frequency band where the beam searching or beamtransmission is performed for the area determined based on the locationinformation. For example, the location information transmission and thebeam searching or transmission for the area based thereon may beperformed in a frequency band of 6 GHz or higher. For controlinformation, transmission of multiple wideband beams or sharp beamsshould be supported. That is, a rule may be defined such that for thecontrol information transmitted with the location information, themultiple beam transmission should be performed. In addition, if UEsobtains their location information through the multiple beamtransmission, the UEs can transmit and receive data signals only in alimited direction on the basis of their higher-layer information(locations, speeds, and specific events (for example, lane change,intersection entrance, accident occurrence, etc.)).

The location information may be valid only during a time periodindicated by a time stamp, which is transmitted together with thelocation information. The time period indicated by the time stampdepends on the speed of the UE that transmits the location information.For example, when a UE moves at a very high speed, the UE may indicate avery short time period through the time stamp because the locationinformation also changes rapidly so that the validity thereof can beguaranteed. If the received location information exceeds a predeterminedtime period, the UE may determine that the corresponding location isinaccurate and then perform the previous omni-directional beam searchingand beamforming.

At least one of a beam direction, a preferential beam searchingdirection, and a beam width for the beam searching or beam transmissionmay be determined according to at least one of a location, a speed, amoving direction, a service, a packet latency requirement, etc. Thisoperation may be performed by the first UE, which receives the locationinformation of the second UE and then performs the beam searching orbeam transmission for the area determined based thereon. Alternatively,the operation may be performed regardless of the reception of thelocation information. Hereinafter, the configuration that depends onindividual elements such as a location, a speed, a moving direction, aservice, a packet latency requirement, etc. will be described in detail.

Depending on the location and/or speed of a UE, beamforming directionsor beam searching candidates may be limited, or the order of beams to bepreferentially searched for during the beam searching or beam width maybe changed. For example, the directions of beams to be searched forand/or preferential beams may depend on the place where the UE is, forexample, a parking lot, a highway, and a normal road. In other words,according to the location of the UE or the place at which the UE is(i.e., place characteristics) (in this case, the place characteristicsmay include at least one of the number of statistical UEs at the placewhere the UE is, a statistical moving direction, and a statisticalspeed), the configuration setting of the beam directions/preferentialbeam directions/beam widths/beam searching areas may vary.

As a particular example, if a UE is in a parking lot, the UE shouldperform the beam searching in all directions. If a UE is on a normalroad, the UE should perform the beam searching in the rear direction atan angle of 60 degrees. If a UE is on a highway, the UE should performthe beam searching in the front and rear directions at an angle of 30degrees. In a parking lot, since a UE may move slowly, a collision withanother vehicle may occur in all directions, and thus the UE can performthe beam searching in all directions. If a UE is on a normal road orhigh way where the average UE speed is relatively high, the UE'sinteresting range may be changed. For example, compared to the normalroad where many neighboring vehicles cut into lanes or change theirpaths, such sudden changes do not frequently occur on the high way.Thus, the UE may reduce the beam searching area on the highway. In otherwords, when the first UE is on a highway, the preferential beamsearching direction may cover a smaller area than when the first UE ison a normal road. Although the beam searching area can be adjusted asdescribed above, the beam width used for the initial beam searching canalso be adjusted. For example, as the UE speed increases, the beam widthmay decrease. On the contrary, as the UE speed decreases, the beam widthmay increase. That is, when the first UE is on a highway, the beam widthmay be smaller than when the first UE is on a normal road.

As another example, as shown in FIG. 12(a), as the first UE's speedincreases, the beam width for the beam searching may decrease. Sincewhen a UE moves at a low speed, the UE can easily change its movingdirection, the UE should search for beams in a wide area. On thecontrary, when a UE moves at a high speed, the UE can search for beamsin a small area.

As shown in FIG. 12(b), the moving direction of the first UE may changeat least one of a beam direction, a preferential beam searchingdirection, and a beam width. Depending on the moving direction of a UE(heading) (for example, the moving direction may be determined based onthe operation of a turn signal indicator and/or by a sensor mounted in avehicle), beamforming directions or beam searching candidates may belimited, or the order of beams to be preferentially searched for duringthe beam searching or beam width may be changed. By transmitting aspecific message to another UE existing in the same direction as that inwhich the HE is moving, the UE can rapidly transmit and receive safetymessages.

In addition, depending on the type of a provided service, beam searchingcandidates may be limited, or the order of beams to be preferentiallysearched for during the beam searching may be changed. For example, fora safety message, the beam searching/beam transmission and reception maybe performed in a large area. For a service such as See Through, thebeam searching/beam transmission and reception may be performed in thefront and rear directions. In other words, when the service relates to asafety message, the beam width increases compared to when the servicerelates to other messages rather than the safety message.

Moreover, depending on a packet latency requirement, at least one of abeam direction, preferential beam searching direction, and a beam widthmay be changed. For example, if a packet has a low latency requirement,it needs to be quickly transmitted to neighboring UEs, and thus the beamsearching may be performed using a wide beam. That is, when the packetlatency requirement is low, the beam width decreases compared to whenthe packet latency requirement is high. As another example, the numberof beam searching steps may be changed according to the latencyrequirement. For example, assuming that hierarchical beam searching isperformed, a UE with a low latency requirement may perform two-step beamsearching, and a UE with a high latency requirement may performthree-or-four-step beam searching more accurately. To this end, UEs mayexchange information on their latency requirements through physical orhigher layer signals, and more specifically, the UEs may signal to eachother information on the number of beam searching steps.

According to the above-described methods, it is possible to reduce theUE implementation complexity by decreasing the complexity, searchingtime, and searching order of beam searching. By doing so, even when UEsmove at high speeds, the beam searching can be rapidly performed, andthus services can be smoothly provided.

FIG. 13 illustrates an example of a beam transmission/searching method.

According to this method, when a UE changes a lane or is in anintersection (a specific area), the UE may perform beam searching and/orsharp beam repetition transmission in multiple directions (in a lesslimited and more flexible manner). Referring to FIG. 13, assuming thatUEs A and B drive on a straight road and do not need to receiveinformation on the opposite lane due to a median strip, UEs A and Btransmit and receive beams with respect to the driving lane and adjacentlanes. Since UE C is going to enter the intersection, UE Ctransmits/searches for beams in all possible directions. If a UE doesnot change its lane, the UE may perform beam searching and/or sharp beamrepetition transmission (of data) in a specific (limited) direction.This method could be interpreted to mean that the UE transmits abroadcast message.

Meanwhile, the same method may be used when Vehicle UEs (V-UEs) transmitand receive signals to and from an eNB or RSU. To this end, the V-UEsshould be able to obtain the location information of an adjacent eNB orRSU. The eNB or RSU can broadcast the location information periodically,and in this case, the location information may be broadcast at othercarrier frequencies instead of a mmWave band. When a V-UE transmits andreceives signals to and from an eNB or RSU using location information,the V-UE may perform the beam transmission/searching in a limiteddirection.

In the case of a broadcast message, a UE may perform the beamtransmission/searching only in the UE's moving direction or interestingdirections. Depending on the location, speed, and moving direction of a(transmitting) UE and a specific event of the transmitting UE (forexample, lane change, intersection entrance, accident occurrence, etc.),the direction of a transmission beam and the searching direction for areceived beam may be determined.

Depending on higher layer information (the location, speed, and movingdirection of a (transmitting) UE and a specific event of thetransmitting UE (for example, lane change, intersection entrance,accident occurrence, etc.)), at least one of the number of times of beamtransmission, beam directions, the number of times of reception beamsearching, and direction information may be determined in advance.Alternatively, a network may signal at least one of the number of timesof beam transmission, beam directions, the number of times of receptionbeam searching, and direction information (to be used by a UE), whichdepend on higher layer information (the location, speed, and movingdirection of a (transmitting) UE and a specific event of thetransmitting UE (for example, lane change, intersection entrance,accident occurrence, etc.)) to the UE through a higher layer or physicallayer signal.

Since each embodiment of the above-described proposed method can beconsidered as one method for implementing the present invention, it isapparent that each embodiment can be regarded as a proposed method. Inaddition, the present invention can be implemented not only using theproposed methods independently but also by combining (or merging) someof the proposed methods. Moreover, a rule may be defined such thatinformation on whether the proposed methods are applied (or informationon rules related to the proposed methods) should be transmitted from aneNB to a UE through a predefined signal (e.g., physical layer signal,higher layer signal, etc.), a transmitting UE signals the information toa receiving UE, or a receiving UE requests a transmitting UE to transmitthe information.

Device Configurations According to Embodiments of the Present Invention

FIG. 14 is a diagram illustrating configurations of a transmission pointdevice and a UE device according to an embodiment of the presentinvention.

Referring to FIG. 14, a transmission point device 10 may include areceiving module 11, a transmitting module 12, a processor 13, a memory14, and a plurality of antennas 15. The plurality of the antennas 15 maymean that the transmission point device supports MIMO transmission andreception. The receiving module 11 may receive various signals, data andinformation from a UE in uplink. The transmitting module 12 may transmitvarious signals, data and information to the UE in downlink. Theprocessor 13 may control overall operation of the transmission pointdevice 10.

The processor 13 of the transmission point device 10 according to anembodiment of the present invention may perform the processes requiredin the above-described embodiments.

In addition, the processor 13 of the transmission point device 10 mayperform a function of processing information received by thetransmission point device 10, information to be transmitted by thetransmission point device 10, and the like. The memory 14 may store theprocessed information during a prescribed time period and be substitutedwith a component such as a buffer (not shown in the drawing) or thelike.

Referring to FIG. 14, a UE device 20 may include a receiving module 21,a transmitting module 22, a processor 23, a memory 24, and a pluralityof antennas 25. The plurality of antennas 25 may mean that the UE devicesupports MIMO transmission and reception. The receiving module 21 mayreceive various signals, data and information from an eNB in downlink.The transmitting module 22 may transmit various signals, data andinformation to the eNB in uplink. The processor 23 may control overalloperation of the UE device 20.

The processor 23 of the UE device 20 according to an embodiment of thepresent invention may perform the processes required in theabove-described embodiments. Specifically, the processor may beconfigured to: receive location information from a second UE through thereceiving module; and perform either or both of beam searching and beamtransmission for an area determined based on the received locationinformation. In this case, at least one of a beam direction, apreferential beam searching direction, and a beam width for the beamsearching or beam transmission may be determined according to at leastone of a location, a speed, a moving direction, a service, and a packetlatency requirement of a first UE.

In addition, the processor 23 of the UE device 20 may perform a functionof processing information received by the UE device 20, information tobe transmitted by the UE device 20, and the like. The memory 24 maystore the processed information during a prescribed time period and besubstituted with a component such as a buffer (not shown in the drawing)or the like.

The configurations of the transmission point device and the UE devicemay be implemented such that the above-described embodiments can beindependently applied or two or more thereof can be simultaneouslyapplied, and redundant description is omitted for clarity.

The description of the transmission point device 10 in FIG. 14 may beequally applied to a relay as a downlink transmission entity or anuplink reception entity, and the description of the UE device 20 in FIG.14 may be equally applied to a relay as a downlink reception entity oran uplink transmission entity.

The embodiments according to the present invention may be implemented byvarious means, for example, hardware, firmware, software, or theircombination.

In a hardware configuration, the embodiments of the present disclosuremay be achieved by one or more application specific integrated circuits(ASICs), digital signal processors (DSPs), digital signal processingdevices (DSPDs), programmable logic devices (PLDs), field programmablegate arrays (FPGAs), processors, controllers, microcontrollers,microprocessors, etc.

In a firmware or software configuration, a method according toembodiments of the present disclosure may be implemented in the form ofa module, a procedure, a function, etc. Software code may be stored in amemory unit and executed by a processor. The memory unit is located atthe interior or exterior of the processor and may transmit and receivedata to and from the processor via various known means.

As described before, a detailed description has been given of preferredembodiments of the present disclosure so that those skilled in the artmay implement and perform the present disclosure. While reference hasbeen made above to the preferred embodiments of the present disclosure,those skilled in the art will understand that various modifications andalterations may be made to the present disclosure within the scope ofthe present disclosure. For example, those skilled in the art may usethe components described in the foregoing embodiments in combination.The above embodiments are therefore to be construed in all aspects asillustrative and not restrictive. The scope of the disclosure should bedetermined by the appended claims and their legal equivalents, not bythe above description, and all changes coming within the meaning andequivalency range of the appended claims are intended to be embracedtherein.

Those skilled in the art will appreciate that the present disclosure maybe carried out in other specific ways than those set forth hereinwithout departing from the spirit and essential characteristics of thepresent disclosure. The above embodiments are therefore to be construedin all aspects as illustrative and not restrictive. The scope of thedisclosure should be determined by the appended claims and their legalequivalents, not by the above description, and all changes coming withinthe meaning and equivalency range of the appended claims are intended tobe embraced therein. It is obvious to those skilled in the art thatclaims that are not explicitly cited in each other in the appendedclaims may be presented in combination as an embodiment of the presentdisclosure or included as a new claim by a subsequent amendment afterthe application is filed.

INDUSTRIAL APPLICABILITY

The above-described embodiments of the present disclosure are applicableto various mobile communication systems.

What is claimed is:
 1. A method for performing beam searching or beamtransmission by a first user equipment, UE, in a wireless communicationsystem, the method comprising: receiving location information from asecond UE; and performing either or both of the beam searching and beamtransmission for an area determined based on the received locationinformation, wherein at least one of a beam direction, a preferentialbeam searching direction, and a beam width for the beam searching orbeam transmission is determined according to at least one of a location,a speed, a moving direction, a service, and a packet latency requirementof the first UE.
 2. The method of claim 1, wherein a frequency band inwhich the location information is received is lower than a frequencyband in which the either or both of the beam searching and beamtransmission is performed.
 3. The method of claim 1, wherein thelocation information is included in control information.
 4. The methodof claim 1, wherein the location information is valid only during atimer period indicated by a time stamp transmitted together with thelocation information.
 5. The method of claim 1, wherein when the firstUE is in a parking lot, the beam direction includes all directions. 6.The method of claim 1, wherein when the first UE is on a highway, thepreferential beam searching direction covers a smaller area than whenthe first UE is on a normal road.
 7. The method of claim 1, wherein whenthe first UE is on a highway, the beam width is smaller than when thefirst UE is on a normal road.
 8. The method of claim 1, wherein as thespeed of the first UE increases, the beam width for the beam searchingdecreases.
 9. The method of claim 1, wherein the moving direction of thefirst UE changes the at least one of the beam direction, thepreferential beam searching direction, and the beam width.
 10. Themethod of claim 1, wherein the moving direction is determined by atleast one of a turn signal indicator of the first UE and a second of thefirst UE.
 11. The method of claim 1, wherein when the service relates toa safety message, the beam width increases compared to when the servicerelates to other messages rather than the safety message.
 12. The methodof claim 1, wherein when the packet latency requirement is low, the beamwidth decreases compared to when the packet latency requirement is high.13. The method of claim 1, wherein the first UE is a Vehicle UserEquipment (VUE).
 14. A first user equipment, UE, for performing beamsearching or beam transmission in a wireless communication system,comprising: a transmitting module; a receiving module; and a processor,wherein the processor is configured to receive location information froma second UE through the receiving module and perform either or both ofthe beam searching and beam transmission for an area determined based onthe received location information, and wherein at least one of a beamdirection, a preferential beam searching direction, and a beam width forthe beam searching or beam transmission is determined according to atleast one of a location, a speed, a moving direction, a service, and apacket latency requirement of the first UE.